Unit for sterilizing web-fed material on a machine for packaging pourable food products

ABSTRACT

A unit for sterilizing a web ( 2 ) of packaging material on a machine ( 1 ) for packaging pourable food products, the unit having a bath ( 7 ) containing a sterilizing agent, in which the web ( 2 ) is fed continuously; a process chamber ( 8 ) connected to an outlet ( 12 ) of the bath ( 7 ), and housing drying means ( 17 ) for removing residual sterilizing agent from the web ( 2 ); an aseptic chamber ( 25 ) communicating with the process chamber ( 8 ) via an opening ( 27 ) for passage of the web ( 2 ), and in which the web ( 2 ) is folded and sealed longitudinally to form a tube ( 29 ) which is filled continuously with the product for packaging; and an air processing circuit ( 24 ) for controlling process conditions; the circuit ( 24 ) draws air from the process chamber ( 8 ) through an orifice ( 54 ), the opening of which is adjustable, during operation of the machine, by a shutter ( 55 ) to maintain a pressure value greater than a predetermined minimum value in the aseptic chamber ( 25 ).

TECHNICAL FIELD

The present invention relates to a unit for sterilizing web-fed materialon a machine for packaging pourable food products.

BACKGROUND ART

Machines for packaging pourable food products—such as fruit juice, wine,tomato sauce, pasteurized or long-storage (UHT) milk, etc.—are known, onwhich packages are formed from a continuous tube of packaging materialdefined by a longitudinally sealed web.

The packaging material has a multilayer structure comprising a layer ofpaper material covered on both sides with layers of heat-seal material,e.g. polyethylene. And, in the case of aseptic packages for long-storageproducts, e.g. UHT milk, the packaging material comprises a layer ofbarrier material defined, for example, by aluminium foil, and which issuperimposed on a layer of heat-seal plastic material, and is in turncovered with another layer of heat-seal plastic material eventuallydefining the inner face of the package and therefore contacting the foodproduct.

To produce aseptic packages, the web of packaging material is unwoundoff a reel and fed through a sterilizing unit, in which it issterilized, for example, by immersion in a bath of liquid sterilizingagent, such as a concentrated hydrogen peroxide and water solution.

More specifically, the sterilizing unit comprises a bath filled, in use,with the sterilizing agent, into which the web is fed continuously. Thebath conveniently comprises two vertical parallel branches connected atthe bottom to define a U-shaped path long enough to ensure the packagingmaterial is treated for a sufficient length of time. For effectivetreatment in a relatively short time, and therefore to reduce the sizeof the sterilizing chamber, the sterilizing agent must be maintained ata high temperature, e.g. around 70° C.

The sterilizing unit also comprises a process chamber located over thebath, and in which the web of packaging material is dried; and anaseptic chamber, in which the web is folded and sealed longitudinally toform a tube, which is then filled continuously with the product forpackaging.

More specifically, in the process chamber, the web is processed toremove any residual sterilizing agent, the acceptable amount of which inthe packaged product is governed by strict standards (the maximumpermissible amount being in the region of a few fractions of apart permillion).

Such processing normally comprises mechanical removal of any drops onthe material, followed by air drying.

The drops may be removed, for example, by feeding the material through apair of wringing rollers conveniently located close to the processchamber inlet, and downstream from which the material is still coveredwith a film of sterilizing agent, but has no macroscopic drops.

Drying may be performed by means of air knives facing opposite faces ofthe material, supplied with air from the sterile environment, e.g. bymeans of a recirculating conduit as described in EP-A-1 050 467, andwhich provide for removing residual traces of sterilizing agent byevaporation.

Alternatively, complete drying may be achieved in a low drying channel,through which the process chamber communicates with the aseptic chamber.

Before leaving the aseptic chamber, the web is folded into a cylinderand sealed longitudinally to form, in known manner, a continuous,longitudinally sealed, vertical tube. In other words, the tube ofpackaging material forms an extension of the aseptic chamber, and isfilled continuously with the pourable food product and then fed to aforming and (transverse) sealing unit for forming the individualpackages, and on which the tube is gripped and sealed transverselybetween pairs of jaws to form aseptic pillow packs.

The pillow packs are separated by cutting the seals between the packs,and are then fed to a final folding station where they are foldedmechanically into the finished shape.

Packaging machines of the above type are used widely and satisfactorilyin a wide range of food industries for producing aseptic packages fromweb-fed packaging material. Performance of the sterilizing unit, inparticular, ensures ample conformance with standards governing sterilityof the packages.

A need for further improvement, however, is felt within the industryitself, particularly as regards pressure control in the sterilizingunit.

In known machines, the pressure and temperature conditions in theprocess and aseptic chambers are normally controlled by a closed airprocessing circuit, which draws air from the process chamber and feedsit back into the aseptic chamber.

To ensure sterility of the environment defined by the process andaseptic chambers, both chambers must be maintained at higher thanatmospheric pressure, so that any leakage can only occur outwards, i.e.sterile air can leak from the machine, but no non-sterile air can leakfrom the outside environment into the machine. Moreover, to ensureone-way airflow from the aseptic chamber to the process chamber, atleast a roughly 10 mmH₂O pressure difference must be maintained betweenthe two chambers.

In known machines, the pressure values in the aseptic and processchambers are substantially defined by design conditions, are ensured byappropriate calibrated leakage between the two chambers and between theprocess chamber and the outside, and are simply monitored, so that, ifthey are too low, e.g. due to in-service sealing defects, the machine,and therefore production, must be stopped for the necessary steps to betaken.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a unit forsterilizing packaging material, designed to eliminate the aforementioneddrawback, i.e. which provides for controlling pressure in the asepticchamber and process chamber with no stoppage in production.

According to the present invention, there is provided a sterilizing unitfor sterilizing a web of packaging material on a machine for packagingpourable food products, the sterilizing unit comprising:

a bath containing a sterilizing agent, in which said web is fedcontinuously;

an aseptic environment comprising a process chamber connected to anoutlet of said bath and housing drying means for removing residualsterilizing agent from said web; and an aseptic chamber communicatingwith said process chamber via an opening for the passage of said web,and in which said web is folded and sealed longitudinally to form a tubewhich is filled continuously with the product for packaging; and

an air processing circuit for controlling the process conditions in saidaseptic environment, and comprising suction means for drawing air fromsaid process chamber, air processing means, and means for feedingprocessed air into said aseptic chamber;

characterized by comprising valve means interposed between said processchamber and said suction means of said air processing circuit, and whichcan be activated during operation of said machine to control thepressure conditions in said aseptic environment.

In a preferred embodiment of the present invention, the sterilizing unitcomprises a transition chamber communicating with the inlet of the bathand with the suction means; and the valve means comprise an orificeinterposed between the process chamber and the transition chamber, and aclosing member which is movable to adjust the opening of the orificebetween the two chambers, and so adjust the pressure in the asepticenvironment during production.

Preferably, the closing member is movable between an open position, anda fully-closed position isolating the process chamber from the outsideenvironment, so that, during production stoppages, air can be drawnthrough the bath, which, during stoppages, is empty. This thereforeprovides for ventilating and cooling the packaging material, thusreducing impregnation of the edges of the web with sterilizing agentwhen production is started up again.

A barrier is provided between the process chamber and aseptic chamber toensure a pressure difference between the two chambers, and defines,between the chambers, an opening through which the packaging material isfed.

According to a further preferred characteristic of the presentinvention, said opening is asymmetrical with respect to the travelingplane of the packaging material, i.e. is higher on the side facing oneof the two faces of the material, and is preferably higher on theunderside.

As such, the sterilizing unit can also be used for processing packagingmaterial fitted with opening devices, which are fed through the higherside of the opening, while the other, lower, side ensures a sufficientpressure drop between the two chambers.

Even more preferably, the packaging material is fed horizontally throughthe opening, and is then guided by a roller housed in the asepticchamber, immediately downstream from the opening; and the opening isdefined, on the higher side, e.g. downwards, by a partition shaped toget close to the roller, so as to define, for the airflow from theaseptic chamber to the process chamber, a barrier ensuring the requiredpressure drop.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1 shows a diagram of a machine for packaging pourable food productsand featuring a sterilizing unit in accordance with the invention;

FIGS. 2 and 3 show partial schematic views of the sterilizing unitaccording to the invention in two different operating conditions.

BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in FIG. 1 indicates as a whole a machine for packaging pourablefood products, and for continuously producing aseptic packages of apourable food product from a web-fed packaging material 2 (hereinafterreferred to simply as “web 2”).

Machine 1 comprises a sterilizing unit 3 for sterilizing web 2, and towhich web 2 is fed off a reel (not shown) along a path P1.

Machine 1 also comprises a unit 4, located upstream from sterilizingunit 3, for applying closable opening devices 5 to web 2, and which isconveniently defined by a known station for injection molding plasticmaterial, and through which web 2 is fed in steps. On leaving unit 4,the web comprises a succession of equally spaced opening devices 5(shown schematically in FIG. 1 on only a portion of web 2) projectingfrom one face of web 2.

Sterilizing unit 3 comprises a transition chamber 6, into which web 2 isfirst fed; a sterilizing bath 7 containing a liquid sterilizing agent,e.g. a solution of 30% hydrogen peroxide (H₂O₂) and water, through whichweb 2 is fed; and a process chamber 8, in which web 2 is dried asexplained in detail later on.

Bath 7 is substantially defined by a U-shaped conduit, which is filled,in use, with sterilizing agent to a predetermined level, and which inturn is defined by two vertical, respectively inlet and outlet, branches9, 10 having respective top openings 11, 12, which respectively definethe web 2 inlet and outlet of bath 7, and communicate respectively withtransition chamber 6 and process chamber 8. The two branches areconnected at the bottom by a bottom portion 13 of bath 7, in which ishoused a horizontal transmission roller 14.

Inside bath 7, web 2 therefore travels along a U-shaped path P2, thelength of which is defined to ensure the packaging material is kept longenough in the sterilizing agent.

Bath 7 is connected to a known peroxide control circuit 15 (notdescribed in detail), and is maintained, in use, at a controlledtemperature, e.g. of about 70° C.

Process chamber 8 (FIGS. 2 and 3) is located over transition chamber 6,is separated from transition chamber 6 by partitions 16, and housesdrying means indicated as a whole by 17 and for removing residualsterilizing agent from web 2.

Drying means 17 comprise two parallel, horizontal, idle wringing rollers18—at least one of which is covered with a relatively softmaterial—located close to the inlet of process chamber 8, on oppositesides of web 2, and which cooperate with and exert pressure onrespective opposite faces of web 2 to wring any drops of sterilizingagent out and back into bath 7.

Wringing rollers 18 conveniently comprise respective small-diameterintermediate portions (not shown) corresponding with the longitudinalintermediate portion of web 2, as illustrated in EP-A-1 050 468, topermit the passage of opening devices 5 without interfering with therollers.

Downstream from wringing rollers 18, web 2 is deflected along ahorizontal path P3 by a transmission roller 19.

Drying means 17 also comprise a known so-called “air knife” 21 (shownschematically), which is defined by a nozzle 22 for directing an air jeton to the face of web 2 eventually defining, in use, the inside of eachpackage, and by two plates 23 for directing the jet, in use,substantially parallel to, but in the opposite direction to thetraveling direction of, web 2.

Nozzle 22 forms part of an air processing circuit 24 described in detaillater on.

Sterilizing unit 3 also comprises a vertical aseptic chamber or tower 25having a top portion 26 communicating with process chamber 8 through anopening 27 for the passage of web 2, and an elongated bottom portion 28,in which web 2 is folded longitudinally into a cylinder and sealedlongitudinally to form a continuous tube 29 of packaging material with avertical axis A. Aseptic chamber 25 and process chamber 8 togethertherefore define an aseptic environment 30.

Top portion 26 houses a number of transmission and guide rollers 31, 32,33 for guiding web 2 from horizontal path P3 to a vertical path P4parallel to axis A of tube 29. More specifically, roller 31 is poweredand located immediately downstream from opening 27; roller 32 is idle,and defines a tensioner; and roller 33 is also idle, and provides forguiding and deflecting web 2 downwards.

Tube 29, formed downstream from roller 33 in known manner not described,is filled continuously with the product by a fill conduit 34, and is fedout downwards through a bottom opening 35 in aseptic chamber 25, thussubstantially forming an extension of the aseptic chamber.

Machine 1 comprises a known forming and transverse sealing unit 36 (notshown in detail), in which the tube 29 of packaging material is grippedand sealed transversely by pairs of jaws 37 to form aseptic pillow packs38, which are eventually cut and folded in known manner to form theindividual packages.

Air processing circuit 24 comprises a suction conduit 40 communicatingwith transition chamber 6; and a known processing unit 41 (not shown indetail) having an inlet connected to conduit 40, and an outlet connectedto a conduit 42 for feeding processed air into sterilizing unit 3.Processing unit 41 conveniently comprises, in known manner, a compressor43; purifying means 44 for removing residual sterilizing agent; andheating means 45 for heating and sterilizing the air. Conduit 42 isconnected to an inlet of a three-way distributor 46 having two outlets46 a, 46 b connected respectively to nozzle 22 of air knife 21 by aconduit 47, and to one or more air inlets 48 in the bottom portion ofaseptic chamber 25 by a conduit 49. Distributor 46 has two shutters 50,51, which can be operated independently, e.g. by respectiveservoactuators (not shown), and provide for controlling airflow alongconduits 47, 49; and an electric heater 52 is housed in conduit 47.

Transition chamber 6 communicates with the outside environment throughan orifice 53, which has a cover normally closed by gravity, but openedunder low pressure during operation of the machine, and which defines,for circuit 24, a zero pressure reference point with respect to theoutside environment.

Process chamber 8 can communicate with transition chamber 6 through anorifice 54 adjustable by means of a shutter 55.

Shutter 55 is movable—e.g. rotates integrally with a pin 56 controlledby an actuator 57—between an open position (FIG. 2) in which processchamber 8 communicates directly with transition chamber 6, and a closedposition (FIG. 3) in which the two chambers are isolated. The openposition is conveniently adjustable, e.g. by manually adjusting amechanical limit stop 58 of shutter 55, even during operation of themachine.

The pressure in aseptic chamber 25 is detected by a sensor PS1 with areading display 59.

In the event web 2 is fitted with opening devices 5, opening 27 betweenprocess chamber 8 and aseptic chamber 25 must be high enough, on theunderside of web 2 from which opening devices 5 project, to permitpassage of the opening devices. To prevent opening 27, the height ofwhich is conditioned as stated above, from substantially equalizing thepressures in aseptic chamber 25 and process chamber 8, opening 27 is notsymmetrical with respect to the plane of web 2, but is of minimum heightupwards, and is defined downwards by a partition 60 shaped to get closeto roller 31 and so define an airflow barrier and, therefore, aconcentrated fall in pressure.

A programmable control unit 61 of machine 1 controls the processparameters of sterilizing unit 3 on the basis of predetermined referencevalues at each operating stage of the machine, and, in particular,controls heating means 45 of air processing unit 41, peroxide controlcircuit 15, distributor 46, heater 52, and actuator 57.

The process parameters, which may be different variables at differentoperating stages, are defined, for example, by the temperature of theair from unit 41, as detected by a first sensor TS1; the temperature intop portion 26 of aseptic chamber 25, as detected by a second sensorTS2; and the air temperature in conduit 47, upstream from nozzle 22, asdetected by a third sensor TS3.

Operation of sterilizing unit 3 will now be described with reference totwo typical operating conditions: production and short stoppages ofmachine 1.

During production (FIG. 2), bath 7 is full of sterilizing solution, andweb 2 is fed through the bath, is dried in process chamber 8, and issealed longitudinally into a tube in aseptic chamber 25.

In the above operating condition, distributor 46 is positioned to partlyclose outlet 46 b connected to conduit 49, so as to feed a substantialportion, e.g. 40%, of flow to nozzle 22, and the rest, e.g. 60%, toaseptic chamber 25. The air temperature at the outlet of unit 41 is setto roughly 120° C., and heater 52 is controlled, on the basis offeedback from sensor TS3, to supply nozzle 22 with air at roughly 180°C.

Shutter 55 is kept open, so that process chamber 8 communicates directlywith suction conduit 40 of air processing circuit 24; and opening 27 andthe flow section of orifice 54, when shutter 55 is open, are sized tomaintain a pressure of about 10–20 mmH₂O in process chamber 8, and about20–30 mmH₂O in the aseptic chamber, with a roughly 10 mmH₂O pressuredrop through opening 27.

The above overpressure values with respect to the environment aresufficient to prevent entry of external agents, but low enough toprevent substantial leakage of sterilizing-agent-contaminated air fromcontaminating the workplace. The pressure drop through opening 27ensures continuous one-way flow from aseptic chamber 25 to processchamber 8.

The pressure in aseptic chamber 25 during production is detected bysensor PS1.

In the event the pressure in aseptic chamber 25 falls towards a minimumsafety value, e.g. due to poor sealing, this can be corrected duringproduction by manually adjusting limit stop 58 to adjust, and inparticular reduce, the flow section of orifice 54.

During short production stoppages for any routine servicing of machine1, web 2 is stopped and bath 7 emptied.

In this condition, distributor 46 is set to fully open outlet 46 b, andto partly close outlet 46 a, so that flow is substantially suppliedentirely to aseptic chamber 25, and a minimum portion, of about a fewpercent, to air knife 21.

By virtue of its high thermal inertia, aseptic chamber 25 acts as acooler to cool the air flowing through it and through opening 27 intoprocess chamber 8; and, since orifice 54 is closed, the cooled airtravels along bath 7, which is empty, to transition chamber 6, where itis drawn out. This “ventilation” of the bath cools web 2 and reducesso-called “edge wicking”—impregnation of the edges of web 2 withsterilizing agent—when bath 7 is next filled to start up the machine.Edge wicking, which occurs at the edges of web 2 where the paper layeris exposed, can be substantially reduced by reducing the temperature ofbath 7 and web 2 by ventilation as described above, and by loading thesterilizing agent at an appropriately high temperature when the machineis started up.

Clearly, changes may be made to machine 1, and in particular tosterilizing unit 3, without, however, departing from the scope of theaccompanying claims.

In particular, the section of orifice 54 may be closed-loop controlledautomatically to compensate for any fall in pressure in aseptic chamber25.

1. A sterilizing unit for sterilizing a web of packaging material on amachine for packaging pourable food products, the sterilizing unitcomprising: a bath containing a sterilizing agent, in which said web isfed continuously; an aseptic environment comprising a process chamberconnected to an outlet of said bath and housing drying means forremoving residual sterilizing agent from said web; and an asepticchamber communicating with said process chamber via an opening for thepassage of said web, and in which said web is folded and sealedlongitudinally to form a tube which is filled continuously with theproduct for packaging; and an air processing circuit for controlling theprocess conditions in said aseptic environment, and comprising suctionmeans for drawing air from said process chamber, air processing means,and means for feeding processed air into said aseptic chamber;comprising valve means interposed between said process chamber and saidsuction means of said air processing circuit, and which can be activatedduring operation of said machine to control the pressure conditions insaid aseptic environment.
 2. A sterilizing unit as claimed in claim 1,comprising a transition chamber communicating with an inlet of the bathand with said suction means; said valve means being interposed betweensaid process chamber and said transition chamber.
 3. A sterilizing unitas claimed in claim 2, wherein said valve means comprise an orificeconnecting said process chamber to said transition chamber; and amovable shutter for adjusting the opening of said orifice.
 4. Asterilizing unit as claimed in claim 3, wherein the shutter is movablebetween an open position wherein said process chamber communicatesdirectly with said transition chamber via said orifice, and a closedposition wherein said process chamber communicates with said transitionchamber via said bath when containing no sterilizing agent.
 5. Asterilizing unit as claimed in claim 4, comprising sensor means fordetecting the pressure in said aseptic environment; and adjusting meansfor adjusting said open position to maintain, in said asepticenvironment, a pressure value at least equal to a predeterminedthreshold value.
 6. A sterilizing unit as claimed in claim 2, comprisingan orifice connecting said transition chamber to the outsideenvironment; said orifice being normally closed, but being opened underlow pressure.
 7. A sterilizing unit as claimed in claim 1, comprisingbarrier means for producing a localized pressure drop between saidaseptic chamber and said process chamber; said barrier means definingsaid opening, through which said web Is fed, between said processchamber and said aseptic chamber.
 8. A sterilizing unit as claimed inclaim 7, for processing a web of packaging material fitted with openingdevices projecting from one face of said web; wherein said opening isasymmetrical with respect to the traveling plane of said web, and ishigher on the side facing the face of said web from which said openingdevices project.
 9. A sterilizing unit as claimed in claim 8, comprisinga guide roller located immediately downstream from said opening; saidbarrier means comprising a partition defining said opening and shaped toget close to said roller.
 10. A sterilizing unit as claimed in claim 1,wherein said drying means comprise at least one nozzle for directing ajet of air on to said web; said means for feeding processed air intosaid aseptic environment comprising a first conduit for feeding air toan air inlet in said aseptic chamber, a second conduit for feeding airto said nozzle, and a distributor having an inlet connected to said airprocessing means, and two outlets connected respectively to said secondconduit and to said first conduit.
 11. A sterilizing unit as claimed inclaim 10, comprising a heater housed in said second conduit.